In the flight control art, attempts have been made in the past to reduce or eliminate the ballistic vulnerability of a flight control by fabricating the cylinder and/or piston as armor utilizing conventional armorplate techniques. Such armor construction is shown in Sliney U.S. Pat. No. 3,566,741 which teaches tubular armorplate formed from an impact-resistant outer armor shell and a slightly softer inner armor shell. Such constructions proved to be unreasonably heavy and large, and therefore, unacceptable for aircraft use and, further, they proved not to provide the deisred ballistic-proof result.
Simmons U.S. Pat. No. 3,884,127 teaches such a control in which both the piston and the cylinder gland through which the piston rod extends are fabricated so as to be shearable so as to prevent piston or piston rod jamming. The Simmons patent has the disadvantage, however, that such flight controls are required to be tested to demonstrate that their structural integrity is such that they can withstand rupture or permanent deformation 2.5 times the normal operating pressure which causes the piston to reciprocate within the cylinder. This test requirement dictates that the area of the piston must be at least 21/2 times the area of the cylinder gland to be able to demonstrate such structural integrity and still result in a cylinder gland which is shearable under normal operating conditions. This requirement that the piston area be at least 21/2 times the gland area results in a control of larger envelope and a greater weight that would otherwise be necessary. This envelope and weight problem is added to by the fact that larger hydraulic chambers formed by such a piston require the use of more operating fluid, with the attendant requirement for a larger fluid supply and dispensing system. In addition, such a large piston generates larger-than-normal operating forces which must be reacted by the remainder of the control system so that the remainder of the control system must be correspondingly strengthened, further increasing the weight problem.
Wallischeck U.S. Application Ser. No. 960,521 filed Nov. 14, 1978, now U.S. Pat. No. 4,211,151, and entitled "Jam Proof Piston", and which is a continuation of U.S. Application Ser. No. 800,766 filed May 26, 1977, now abandoned teaches a concept of enveloping the piston rod of a hydraulic cylinder-piston mechanism in a control system with a sleeve of a material which is either frangible or deformable so that ballistic impact will cause disintegration or deformation thereof, and so that other deformed materials may move into the space left by the disintegrated sleeve or so that other moving parts may further displace the ballistically displaced material so as to permit the piston rod to continue (with respect to the cylinder) following ballistic damage.